1. Technical Field of the Invention
This invention generally relates to the field of recovering lithium from lithium containing solutions. More particularly, the invention relates to the preparation of lithium carbonate from lithium chloride containing brines.
2. Description of the Prior Art
It is known that geothermal brines can include various metal ions, particularly alkali and alkaline earth metals, in varying concentrations, depending upon the source of the brine. Recovery of these metals is important to the chemical and pharmaceutical industries.
Geothermal brines are of particular interest for a variety of reasons. First, geothermal brines provide a source of power due to the fact that hot geothermal pools are stored at high pressure underground, which when released to atmospheric pressure, can provide a flash-steam. The flash-stream can be used, for example, to run a power plant. Additionally, geothermal brines typically contain various useful metals, such as, lithium, lead, silver and zinc, each of which can be recovered from the brine for further use.
Lithium may be recovered from ores, as the ore may be baked with sulfuric acid, and the product leached with water. The resulting lithium sulfate solution is treated with lime and soda ash to remove calcium and magnesium, and lithium is then precipitated as a carbonate. Other known methods for recovering lithium from ores include alkaline methods and ion-exchange methods, each of which can yield solutions of lithium as hydroxide, chloride or sulfate. These methods may also include the removal of calcium and magnesium by treatment with lime and soda ash.
Typically, the economic recovery of lithium from natural, predominantly chloride, brines (which may vary widely in composition), depends not only on the overall lithium content, but also upon the concentrations of interfering ions, particularly calcium and magnesium, which can greatly effect the performance and economics of the lithium recovery. Magnesium can be difficult to remove because it is chemically similar to lithium in solution. Generally, at low concentrations, magnesium may be removed by precipitation with lime as magnesium carbonate. At higher magnesium concentrations, removal with lime is not feasible and various ion exchange and liquid-liquid extraction methods have been proposed.
Although conventional processing of ores and brines makes it possible to eliminate major portions of interfering ions, there remains a need for the simplified removal of interfering ions from brines for the production of lithium carbonate.